Broadband decoupling and off-resonance decoupling are important techniques used in ^13C NMR spectroscopy to improve the appearance and interpretability of carbon spectra. Since ^13C nuclei have relatively low natural abundance and sensitivity, ^13C NMR spectra are generally weaker than ^1H NMR spectra. In addition, carbon atoms are coupled to attached hydrogen nuclei through ^13C–^1H spin-spin interactions, producing multiplet patterns that can make spectra complicated. Decoupling techniques remove or modify these proton-carbon couplings and thereby provide useful information about the structure of organic compounds. In a normal proton-coupled ^13C NMR spectrum, a carbon atom bonded to hydrogen shows splitting according to the number of directly attached hydrogen atoms. A CH3 carbon generally appears as a quartet, a CH2 carbon as a triplet, a CH carbon as a doublet, and a quaternary carbon as a singlet. Although this coupling contains structural information, it also spreads the signal intensity over several lines and makes the spectrum more complicated. Decoupling is therefore employed to simplify the spectrum and, in particular, to enhance the sensitivity of ^13C signals. Broadband decoupling, also called proton broadband decoupling or ^1H decoupling, is the most commonly used method in routine ^13C NMR spectroscopy. In this technique, the proton resonance region is irradiated continuously with a strong radiofrequency field while the ^13C spectrum is being recorded. The irradiation affects essentially all of the protons over a broad range of chemical shifts. As a result, the ^1H spins rapidly change their orientations, and the ^13C nuclei no longer experience a definite, observable spin state of the attached protons. The scalar ^13C–^1H coupling is consequently averaged to zero. The most important result of broadband proton decoupling is that each chemically distinct carbon generally gives a single resonance rather than a multiplet. Thus, a CH3, CH2, CH, or quaternary carbon normally appears as one line in the broadband-decoupled spectrum. For example, in an undecoupled spectrum, a CH2 group can produce a triplet because it is coupled to two equivalent protons. Under broadband decoupling, this triplet collapses into a single peak. Similarly, a CH group gives a doublet in a proton-coupled spectrum but becomes a singlet under broadband decoupling. Broadband decoupling has two major advantages. First, it greatly simplifies the ^13C spectrum. Since each chemically non-equivalent carbon usually produces one signal, the number of resonances can be directly related to the number of different carbon environments in the molecule. This makes broadband-decoupled ^13C NMR particularly useful for identifying organic compounds and determining molecular symmetry. Second, broadband decoupling generally produces a substantial increase in signal intensity through the nuclear Overhauser effect (NOE). Irradiation of protons can transfer polarization to nearby carbon nuclei, increasing the intensity of their ^13C signals. Consequently, broadband-decoupled spectra can